Lepton flavor violation in muonium decay and muon colliders in models with heavy neutrinos
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We study the lepton-flavor-violating reaction $μ^+ e^- \to e^+ e^-$ within two extensions of the standard model that include heavy neutrinos. The reaction is studied in the low energy limit in the form of muonium decay $M\to e^+ e^-$ and in the high energy regime of a muon collider. The two theoretical models we consider are: model I, a typical see-saw model that violates lepton flavor and number by inclusion of extra right handed neutrinos, and model II, a variant where lepton number is conserved and which includes extra right handed as well as left handed neutrinos, singlets under the gauge group. We find for muonium decay into $e^+e^-$ the extremely small result $Br(M\to e^+ e^-) < 10^{-19}$ in both scenarios. Alternatively, for $μ^+ e^-$ collisions up to $\sqrt{s}\sim 50$ GeV we find $σ(μ^+ e^- \to e^+ e^-)< 10^{-5}$ fb, while for energies above the $W^+ W^-$ threshold we find $σ(μ^+ e^- \to W^+ W^-)$ up to 1 fb.
12 pages, 7 figures; new version recalculates the figures and results using the correlated bound on mu-e mixing from $B(μ\to eγ)$ (Eq.34)
12 pages, 7 figures; new version recalculates the figures and results using the correlated bound on mu-e mixing from $B(μ\to eγ)$ (Eq.34)